Field of the Invention
The present invention relates to methods for verifying identification codes used for part identification. More particularly, the present invention relates to a method of verifying the quality of two-dimensional identification marks placed on the surface of a part or component. The overall grade, and diagnostic information is provided to assess the performance of the process used to place the mark on the part.
Description of the Related Art
Automatic identification of products using bar codes has been broadly implemented throughout industrial operations for many years. Traditionally, bar codes or symbols have been printed on labels placed on product packaging and/or material handling trays or containers. The encoded information on the label can be readily identified using various laser scanner or optical readers. Various business operations have come to rely upon the accuracy and availability of data collected from part traceability resulting from automatic identification.
Recent trends are to extend tracking through the full life of a part so that it can be identified from the beginning of its life to the end. To address full life cycle traceability, manufacturers are marking parts with permanent two-dimensional (2D) codes that are marked directly on the part itself, and automatically identifying the part throughout the manufacturing and supply chain operations. This process is known as Direct Part Mark Identification (DPMI).
DPMI is essential for tracking and traceability in highly complex and sensitive assembly systems, such as aerospace and defense systems, medical devices, and electronic assemblies. DPMI permits manufacturers to use traceability data to create a part history through the manufacturing process for later use in supply change management and repair depots.
Part traceability through DPMI improves quality by ensuring that the appropriate processes are performed in the correct sequence on the right parts. DPMI is essential for “error-proofing” initiatives. In addition to eliminating manual part number data entry errors during production operations, DPMI can also assist in data logging for safety, liability, and warranty issues, and to satisfy regulatory requirement for permanently identifying high-value parts that are subject to theft or counterfeiting.
2D codes are typically used for DPMI applications due to the compact size, inherent error correction capabilities, and the amount of information that can be encoded, in comparison to one-dimensional bar codes. In a DPMI application, a 2D code can be marked on the part using several methods, depending upon the material composition, part application, and environmental conditions. Common methods include dot peening, laser and electrochemical etch.
Despite the fact that industries are increasingly adopting DPMI using 2D codes and advanced marking technologies, high read rate DPMI has been difficult to achieve. A limitation to the widespread implementation of DPMI is the inherent difficulty in reading DPMI codes. DPMI codes can be extremely difficult to read, due to low contrast, variations in part surfaces, and partial damage or obliteration from processing and environmental conditions. The application of machine vision technology to hand-held and fixed-mount DPMI readers is essential for a successful implementation of DPMI.
In order to assure that the DPMI code applied to a part will meet the requirements for achieving the highest read rates, it is highly recommended that a code verification system be implemented at the processing station where the code is applied. Verification of a DPMI code is not only a critical factor for downstream reading performance, but it reduces costs associated with rejected parts due to unreadable codes. If a part loses its identity due to the quality of the mark, then the part can often not be used. A verification system will immediately detect a problem with the marking process, such as poor fixturing, damage to the machine, or incorrect settings during configuration or changeover.
A DPMI code verification system typically includes lighting, optics, an image acquisition system, such as a camera, and code verification software. Several verification standards are in use at the present time, such as the AIMI International Symbology Specification for Data Matrix, and the ISO/IEC 15415 International Standard. However, these specifications require an image of a code that can be successfully decoded. Accordingly, there exists a need for a verification method that provides an effective assessment of DPMI codes with diagnostics that provide useful identification of failure modes that can be applied to codes that cannot be decoded due to poor image quality.